Recently, in the photographic market there has been an increasing requirement for rapid photographic processing, and it has become extremely important to meet this requirement.
Silver halide mainly containing silver bromide and having been predominantly used in the past are disadvantageous in principle with respect to rapid processing, since bromide ion to be released upon development of silver bromide has development-inhibiting properties. Thus, from the standpoint of achieving rapid processing, the use of silver halides mainly containing silver chloride is preferable.
So-called "high silver chloride emulsions" containing a high proportion of silver chloride are advantageous in view of attaining suitable rapid processing.
It has been found, however, that the use of high silver chloride emulsions involves the following disadvantage in accelerating photographic processing. That is, though high silver chloride emulsions undergo rapid fixing during a silver-removing step, silver deposit produced as a result of development is much more difficult to bleach than silver deposit produced from low silver chloride emulsions. It has become apparent that this is disadvantageous not only in the case of accelerating and shortening photographic processing, including the silver-removing step, but also in the case of coping with the bleaching difficulty by prolonging the silver-removing time. This is because, in the latter case, the prolonged silver-removing time sometimes negates the shortened or accelerated photographic processing time.
In the bleaching step, a combination of a bleaching bath and a fixing bath or a bleach-fixing bath is used. Suitable bleaching agents to be used in the bleach-fixing bath include organic iron chelating agents, such as iron aminopolycarboxylates showing a moderate oxidizing power not affecting a coexisting fixing agent, such as a silver halide solvent. It has been found that such bleach-fixing baths not having a strong oxidizing power undergo a reduction in oxidizing power particularly when fatigued after processing a large amount of silver halide photographic materials, or when the amount of processing solution used in the foregoing step is increased so that bleaching of silver deposits is delayed and, in an extreme case, a portion of silver deposits can hardly be removed, even by indefinitely prolonged the bleaching time.
In addition, shortening of the exposure time is also important in terms of decreasing the entire photographic processing time, thus improving productivity. Therefore, emulsions to be used must be highly sensitive. However, high silver chloride emulsions are known to have the defect that they easily form fog and possess a low sensitivity, although they can be rapidly developed. Further, intrinsic absorption of the high silver chloride grains occurs in a short wavelength regions; hence, the grains show an extremely weak absorption of visible light in comparison with silver halide grains comprising mainly silver bromide. Particularly, high silver chloride grains containing 99 mol % or more silver chloride are known to scarcely absorb visible light. In order to render silver halide responsive to light in longer wavelength regions than the silver halide-intrinsic absorption region, spectral sensitizing techniques are commonly employed. However, as is different from silver halide emulsions comprising mainly silver bromide, high silver chloride emulsions require spectral sensitization even when used as an emulsion sensitive to light of the blue region. These facts have long been known. Various spectral sensitizing dyes have recently been proposed in Japanese patent application (OPI) Nos. 106,538/83, 107,531/83 and 107,532/83 (U.S. Patent No. 4,469,785); Nos. 107,533/83, 91,444/83; No.95,339/83 (U.S. Patent No. 4,517,284), etc. (the term "OPI" as used herein means an "unexamined published application"). As is different from emulsions comprising mainly silver bromide, high silver chloride emulsions show very poor spectral sensitizing properties, even when subjected to spectral sensitization. For example, the spectral sensitizing agents described in the above-mentioned specifications, which are usually used for emulsions comprising mainly silver bromide and show high sensitizing ability therefor, do not necessarily show high sensitizing ability for high silver chloride emulsions. Further, with respect to spectral sensitizing agents other than those for used for sensitizing emulsions to blue light, many of these spectral sensitizing agents which are effective for emulsions comprising mainly silver bromide have been found to exhibit low sensitizing ability for high silver chloride emulsions. Still further, it has been found that many of the spectral sensitizing agents described in the aforesaid specifications and spectral sensitizing agents used usually for silver halide emulsions comprising mainly silver bromide seriously inhibit bleaching of silver deposits formed in high silver chloride emulsions.
Bleaching of silver deposits depends not only upon the oxidizing power of the bleaching solution, but also upon the shape or form of the silver deposits or the amount of silver deposited. Bleaching difficulty of the silver deposits produced from high silver chloride emulsions in comparison with that from low silver chloride emulsions in attributed to the difference in the shape of silver deposits based on observation of these silver deposits using an electron microscope.
More importantly, bleaching of silver deposits can be delayed or inhibited by some compounds absorbed on the surface of the silver deposits. Silver halide color photographic materials are designed to exert various steps of development processing, from imagewise exposure to development and color formation, and various compounds are incorporated therein for performing such functions. It is important not to cause the aforesaid inhibition of silver removal while meeting these requirements.
It has been observed that the inhibition of removal of silver deposits formed from high silver chloride emulsions is also caused by bromide ion which is usually added to a color developer for assuring uniform development. This bromide ion is considered to change the shape or form of silver deposits.